Measurement of human body surface displacement by breathing using airborne ultrasound

We have studied about non-contact measurement of human body surface displacement by breathing using the ultrasonic pulse-echo method. The displacement by breathing can be determined by continuously measurement of the distance to the human body surface. In the case of a standing human, however, there are the displacement by body movement in addition to that by breathing. Furthermore, displacements by breathing and body movement are equal to or smaller than the wavelength of airborne ultrasound. Therefore, measurement of the displacement by only breathing using airborne ultrasound is typically difficult. We have proposed a measurement method of the displacement by breathing of a standing human. First, the SNR of the echo reflected from the body surface is improved by M-sequence pulse compression in the proposed method. Then, displacements of the front and back of the human body are estimated by tracking phase differences of echo signals. After that, displacement by body movement is canceled by difference between the front and back displacements. In this paper, the displacement by breathing of the standing volunteer was measured by the proposed method. When the volunteer is breathing, the displacement by breathing whose frequency was approximately 0.13 Hz could be measured.